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Waveform display in analog persistance mode

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Waveform display in analog persistance mode

Postby masch » Tue Jan 01, 2013 3:29 pm

Hello,

the oscilloscope i currently use is a Tek TDS3014. A big disadvantage of this scope is its very small memory with only 10k points.

The picoscopes are very intresting to me, especially the 6000 series. But since the Tek is a digital phosphor oscilloscope that tries to emulate the look of an analog scope, i dont want to miss this feature in my future scope. I know that your Software has a persistance mode and also an option that is called "analog intensity" but i do have some questions about it.

If you use the analog intensity setting, are different levels of intensity used for higher and lower frequency content of the actual signal or does the signal only decay after a certain time?

For example, when viewing a video signal (like here http://www.picotech.com/computer-oscilloscope.html) it would be very nice to see a color shaded waveform. Could you supply an image?

The analog intensity mode should also be a mode to find random occuring events such as glitches. But this only makes sense when combined with a high update rate. The Agilent DSOX3000 series claims to have a maximum waveform update rate of about 1 million waveforms per second and there are videos where they measure a waveorm with a glitch every million cycles. These scopes seem to capture this approximatly once every second. Would this be possible with the picoscope in analog intensity mode?? If not, how fast ist the update rate in this mode? It would be nice to see the responsiveness of the display when viewing such a complex waveform in analog intensity mode!

Kind regards,

Markus Schyma
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Re: Waveform display in analog persistance mode

Postby Martyn » Thu Jan 03, 2013 7:40 am

You may wish to take a look at the following video on our TV channel which answers your questions

http://www.picoscope.tv/general/persistence-acquisition-mode.html
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Re: Waveform display in analog persistance mode

Postby masch » Thu Jan 03, 2013 10:31 am

Hello,

i have already watched this video.

The video only shows the analog intensity mode with the decay time set to 5s. For me it would be intresting to see for example an ampitude modulated sine wave with the decay time set to maybe 100ms.

The video also doesen't answer the question about the waveform update rate and if there are different levels of intensity for higher and lower frequency signal content.

As i watched the video again, i noticed that when switching from scope mode to the persistance mode, the window where you can choose the memory depth seems to disappear. Why?

Kind regards

Markus Schyma
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Re: Waveform display in analog persistance mode

Postby Martyn » Thu Jan 10, 2013 9:26 am

The waveform will update according to the specified collection time per waveform, and the rearm time after each waveform has been collected.

When using persistence mode the number of samples collected per waveform is reduced to a lower level, this is why the memory depth menu disappears, and results in a reduction in the amount of data transferred per waveform, a quicker rearm time, and therefore a faster update rate.
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Re: Waveform display in analog persistance mode

Postby masch » Sun Jan 13, 2013 6:18 pm

So for the 6000 series the trigger rearm time can be less than 1µs. When viewing a signal at a timebase of 100ns per division, does it mean i get a waveform update rate of 500.000 waveforms per second on sreen?

In persistence mode, is it possible to change the memory depth? if not, how many samples are used? What is the fastest update rate of a 6000 series oscilloscope i can expect on screen in persistence mode?

What about the analog intensity mode? Are diffrent levels of intensity used? For example, if i take a single shot of a rectangular waveform in this mode, are the edges thinner or is the intensity of the whole signal the same?
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Re: Waveform display in analog persistance mode

Postby Martyn » Mon Jan 14, 2013 9:04 am

The trigger rearm time of 1µs relates to the rapid block mode of operation where multiple waveforms are captured to the memory of the device before downloading to the PC. This is not applicable to persistence mode which uses the normal block mode of operation. The rearm time for this will be dependent on the PC, and data transfer speed over USB, and will be in the ms range.

The number of samples per waveform in persistence mode is limited, this is due to the requirement to process and redraw multiple waveforms as each new one is collected. We are currently working on improving this area although we always have to consider that our devices are used with low end PC's as well as the latest high speed machines.

If you take a single shot waveform then it is possible to select an advanced option colour scheme of Phosphor which will have thinner edges.
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Re: Waveform display in analog persistance mode

Postby alan » Mon Jan 14, 2013 11:10 am

Just to add to the above post, using the PicoScope 6.7 I get 40,000 waveforms per second in persistence mode.

Depending on the persistence mode chosen a single shot square wave will either have less intense vertical edges than the horizontal ones or in color persistence modes the vertical edges will be a "colder" color blue and the horizontal ones a "hotter" red.
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Re: Waveform display in analog persistance mode

Postby masch » Tue Jan 15, 2013 8:23 am

When you say the number of samples in persistence mode is limited, what is the actual number of samples used?
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Re: Waveform display in analog persistance mode

Postby Martyn » Tue Jan 15, 2013 3:59 pm

The current limit is up to 1250 samples per waveform, which may seem low but it is related to the amount of data you can transfer over the USB bus, and the number of waveforms per second you can capture. It is a balancing act between the two and an area we are currently looking at in our software, and is linked to the performance of the PC.
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Re: Waveform display in analog persistance mode

Postby masch » Tue Jan 15, 2013 6:06 pm

1250 samples per waveform seems indeed a bit low.

Doesnt that mean when i capture a signal at a timebase of maybe 100 µs/div (10 divisions total) i get a samplerate of just 1.25 million samples per second which leads to a effective Bandwidth of only 125 kHz?
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Re: Waveform display in analog persistance mode

Postby alan » Wed Jan 16, 2013 8:42 am

If you select a timebase of 100us/div (1millisecond total) then in our scopes with deep memory you can be sampling at the maximum sampling rate in the normal scope mode. For example with the PicoScope 6404B you can be sampling at 5GS/s at this timebase. This will use up only 5 million samples of the 1 billion samples the scope can record. With your TDS3014 with 10K of memory you will only be sampling at 10MS/s.

Persistence mode however is really designed to capture rapidly lots of short duration waveforms. If you use it with a timebase of 1 millisecond across the screen then there is a maximum of 1000 waveforms/second - this is true for all scopes with fast update rates.

Rather than use persistence mode for long timebases (which will limit the sampling rate as you correctly point out) you are better off using the deep memory & zoom tools of the standard scope mode. Another option for finding glitches is to use the rapid block mode to collect 1000s of waveforms with minimal trigger re-arm delay and then use the mask limit tools to scan through them highlighting any that are different to the norm.
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Re: Waveform display in analog persistance mode

Postby Jeff » Tue Jan 29, 2013 12:09 pm

Here is a PAL video waveform that I captured using a PicoScope 3404B. To get the analog intensity grading that masch asked about in his original post, I set up a custom persistence mode including the 'frequency' option. Note that this only works in repeated trigger modes; in single-shot mode, of course, there is no frequency information.

PicoScope6PALPersistenceFreequencyMode.png
PAL video waveform displayed in PicoScope 6 with Persistence Mode
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Re: Waveform display in analog persistance mode

Postby masch » Thu Feb 07, 2013 8:24 am

Thanks for supplying the image of the video waveform.

When using the single-shot mode, wouldn't it be possible to use the information of the rise time (dy/dt of the signal) as a replacement for the frequency? That would be the way an analog oscilloscope phosphor screen works.
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Re: Waveform display in analog persistance mode

Postby Martyn » Tue Feb 12, 2013 2:44 pm

Persistence mode requires multiple waveforms so will not work in single shot, the option disappears form the drop down.
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